Reduce how often LayoutSVGShape::updateShapeFromElement is called

Source/core/layout/svg/LayoutSVGRect.cpp

Index: Source/core/layout/svg/LayoutSVGRect.cpp
diff --git a/Source/core/layout/svg/LayoutSVGRect.cpp b/Source/core/layout/svg/LayoutSVGRect.cpp
index 18b0ccd737b67602e2f4f40fe69236ed49f814fe..d5890dcc06eb45aad4afea34bc4dfaa9973e1542 100644
--- a/Source/core/layout/svg/LayoutSVGRect.cpp
+++ b/Source/core/layout/svg/LayoutSVGRect.cpp
@@ -43,37 +43,64 @@ LayoutSVGRect::~LayoutSVGRect()
 {
 }
 
+void LayoutSVGRect::styleDidChange(StyleDifference diff, const ComputedStyle* oldStyle)
+{
+    if (diff.needsFullLayout() && oldStyle) {
+        const SVGComputedStyle& oldSvgStyle = oldStyle->svgStyle();
+        const SVGComputedStyle& svgStyle = style()->svgStyle();
+        if (oldSvgStyle.rx() != svgStyle.rx()
+            || oldSvgStyle.ry() != svgStyle.ry()
+            || oldSvgStyle.vectorEffect() != svgStyle.vectorEffect()
+            || definitelyHasSimpleStroke(oldSvgStyle) != definitelyHasSimpleStroke(svgStyle))
+            setNeedsShapeUpdate();
+    }
+
+    // Superclass will take care of calling clientStyleChanged.
+    LayoutSVGShape::styleDidChange(diff, oldStyle);
+}
+
 void LayoutSVGRect::updateShapeFromElement()
 {
-    // Before creating a new object we need to clear the cached bounding box
-    // to avoid using garbage.
-    m_fillBoundingBox = FloatRect();
-    m_strokeBoundingBox = FloatRect();
     m_usePathFallback = false;
-    SVGRectElement* rect = toSVGRectElement(element());
-    ASSERT(rect);
 
-    SVGLengthContext lengthContext(rect);
+    // Fallback to LayoutSVGShape and path-based hit detection if the rect
+    // has rounded corners or a non-scaling or non-simple stroke.
+    SVGLengthContext lengthContext(toSVGRectElement(element()));
+    if (lengthContext.valueForLength(styleRef().svgStyle().rx(), styleRef(), SVGLengthMode::Width) > 0
+        || lengthContext.valueForLength(styleRef().svgStyle().ry(), styleRef(), SVGLengthMode::Height) > 0
+        || hasNonScalingStroke()
+        || !definitelyHasSimpleStroke(style()->svgStyle())) {
+        LayoutSVGShape::updateShapeFromElement();
+        m_usePathFallback = true;
+        return;
+    }
+
+    clearPath();
+}
+
+void LayoutSVGRect::updateStrokeAndFillBoundingBoxes()
+{
+    SVGLengthContext lengthContext(toSVGRectElement(element()));
     FloatSize boundingBoxSize(
         lengthContext.valueForLength(styleRef().width(), styleRef(), SVGLengthMode::Width),
         lengthContext.valueForLength(styleRef().height(), styleRef(), SVGLengthMode::Height));
 
     // Spec: "A negative value is an error."
-    if (boundingBoxSize.width() < 0 || boundingBoxSize.height() < 0)
+    if (boundingBoxSize.width() < 0 || boundingBoxSize.height() < 0) {
+        m_fillBoundingBox = FloatRect();
+        m_strokeBoundingBox = FloatRect();
         return;
+    }
 
-    // Spec: "A value of zero disables rendering of the element."
-    if (!boundingBoxSize.isEmpty()) {
-        // Fallback to LayoutSVGShape and path-based hit detection if the rect
-        // has rounded corners or a non-scaling or non-simple stroke.
-        if (lengthContext.valueForLength(styleRef().svgStyle().rx(), styleRef(), SVGLengthMode::Width) > 0
-            || lengthContext.valueForLength(styleRef().svgStyle().ry(), styleRef(), SVGLengthMode::Height) > 0
-            || hasNonScalingStroke()
-            || !definitelyHasSimpleStroke()) {
-            LayoutSVGShape::updateShapeFromElement();
-            m_usePathFallback = true;
+    if (m_usePathFallback) {
+        // Spec: "A value of zero disables rendering of the element." so we can skip
+        // the path fallback and rely on the existing bounding box calculation.
+        if (!boundingBoxSize.isEmpty()) {
+            LayoutSVGShape::updateStrokeAndFillBoundingBoxes();
             return;
         }
+        m_usePathFallback = false;
+        clearPath();
     }
 
     m_fillBoundingBox = FloatRect(
@@ -90,8 +117,8 @@ bool LayoutSVGRect::shapeDependentStrokeContains(const FloatPoint& point)
 {
     // The optimized code below does not support non-simple strokes so we need
     // to fall back to LayoutSVGShape::shapeDependentStrokeContains in these cases.
-    if (m_usePathFallback || !definitelyHasSimpleStroke()) {
-        if (!hasPath())
+    if (m_usePathFallback || !definitelyHasSimpleStroke(style()->svgStyle())) {
+        if (!m_usePathFallback)
             LayoutSVGShape::updateShapeFromElement();
         return LayoutSVGShape::shapeDependentStrokeContains(point);
     }
@@ -119,10 +146,8 @@ bool LayoutSVGRect::shapeDependentFillContains(const FloatPoint& point, const Wi
 }
 
 // Returns true if the stroke is continuous and definitely uses miter joins.
-bool LayoutSVGRect::definitelyHasSimpleStroke() const
+bool LayoutSVGRect::definitelyHasSimpleStroke(const SVGComputedStyle& svgStyle) const
 {
-    const SVGComputedStyle& svgStyle = style()->svgStyle();
-
     // The four angles of a rect are 90 degrees. Using the formula at:
     // http://www.w3.org/TR/SVG/painting.html#StrokeMiterlimitProperty
     // when the join style of the rect is "miter", the ratio of the miterLength